Anterior stabilized knee implant

ABSTRACT

A posterior cruciate ligament retaining knee implant prosthesis comprising a femoral component including a medial condyle and a lateral condyle separated from one another by an intercondylar channel adapted to accommodate throughput of a native cruciate ligament, both the medial condyle and the lateral condyle posteriorly terminate individually, the medial condyle including a medial condyle bearing surface and the lateral condyle including a lateral condyle bearing surface, the femoral component including an anterior cam, and a tibial component including a medial condyle receiver having a medial condyle receiver bearing surface, the tibial component also including a lateral condyle receiver having a lateral condyle receiver bearing surface, the tibial component also including an anterior post.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. patent application Ser. No.12/437,000, which issued as U.S. Pat. No. 8,915,965, entitled “AnteriorStabilized Knee Implant”, which is incorporated by reference herein inits entirety.

RELATED ART

1. Field of the Invention

The present disclosure relates to orthopaedic knee prosthetics and, morespecifically, to anterior stabilized orthopaedic knee prosthetics foruse with posterior cruciate retaining total knee arthroplastyprocedures.

2. Background

The knee is the largest joint in the body. Normal knee function isrequired to perform most everyday activities. The knee is made up of thelower end of the femur, which rotates on the upper end of the tibia, andthe patella, which slides in a groove on the end of the femur. Largeligaments attach to the femur and tibia to provide stability. The longthigh muscles give the knee strength.

The joint surfaces where these three bones touch are covered witharticular cartilage, a smooth substance that cushions the bones andenables them to move easily. The condition of this cartilage lining theknee joint is a key aspect of normal knee function and is important tothe physician when evaluating a potential need for a knee jointreplacement.

All remaining surfaces of the knee are covered by a thin, smooth tissueliner called the synovial membrane. This membrane releases a specialfluid that lubricates the knee, reducing friction to nearly zero in ahealthy knee.

Normally, all of these components work in harmony. But disease or injurycan disrupt this harmony, resulting in pain, muscle weakness, andreduced function.

In addition to the smooth cartilage lining on the joint surfaces, thereare two smooth discs of cartilage that cushion the space between thebone ends. The inner disc is called the medial meniscus, while the discon the outer side of the knee joint is called the lateral meniscus. Therole of the menisci is to increase the conformity of the joint betweenthe femur and the tibia. The menisci also play an important function asjoint shock absorbers by distributing weight-bearing forces, and inreducing friction between the joint segments.

There are also four major ligaments that play an important part instability of the knee joint. The Medial Collateral Ligament (MCL) andthe Lateral Collateral Ligament (LCL) are located on opposing sides onthe outside of the joint. The Anterior Cruciate Ligament (ACL) and thePosterior Cruciate Ligament (PCL) are more centrally located ligamentswithin the joint. The ACL attaches to the knee end of the Femur, at theback of the joint and passes down through the knee joint to the front ofthe flat upper surface of the Tibia. It passes across the knee joint ina diagonal direction and with the PCL passing in the opposite direction,forms a cross shape, hence the name cruciate ligaments.

Total knee replacement (TKR), also referred to as total kneearthroplasty (TKA), is a surgical procedure where worn, diseased, ordamaged surfaces of a knee joint are removed and replaced withartificial surfaces. Materials used for resurfacing of the joint are notonly strong and durable but also optimal for joint function as theyproduce as little friction as possible.

The “artificial joint or prosthesis” generally has three components: (1)a distal femoral component usually made of a biocompatible material suchas metal alloys of cobalt-chrome or titanium; (2) a proximal tibialcomponent also made of cobalt chrome or titanium alloy; and a bearingcomponent disposed there between usually formed of a plastic materiallike polyethylene.

In total knee arthroplasty (TKA) there are three main types of implants:The first main type is the posterior cruciate retaining (PCR) total kneearthroplasty, where the surgeon retains the posterior cruciate ligamentand sacrifices the anterior cruciate ligament. The second main type isthe posterior stabilizing (PS) total knee arthroplasty, where thesurgeon sacrifices both the anterior cruciate ligament (ACL) and theposterior cruciate ligament (PCL). With a PS TKA posterior stabilizationis introduced into the TKA by using a cam/post mechanism. The third maintype is the posterior cruciate sacrificing (PCS) TKA where the surgeonsacrifices both the ACL and the PCL, but does not use a cam/postmechanism for posterior stabilization. Rather, this TKA type usesconstraint in the polyethylene to stabilize the anteroposteriormovement.

Any of the above three main types of TKA implant can have a fixedbearing (FB) design or a mobile bearing (MB) design. With the fixedbearing design, the polyethylene insert is either compression molded orfixed in the tibial tray using a locking mechanism. In a mobile bearingdesign, the polyethylene insert is free to either rotate, translate orboth rotate and translate.

While knee arthroplasty is known as one of the most consistentlysuccessful surgeries offered, there is room for improvement. Forexample, the ACL is sacrificed during the installation of a total kneearthroplasty system, and doing so can have a negative clinical impactfor some patients.

The role of the ACL is to pull the femur in the anterior direction atterminal extension and at full extension. The ACL, attached to thelateral condyle of the femur also works as a tether and keeps thelateral condyle in contact with the lateral meniscus. The PCL pulls thefemur in the posterior direction with increasing flexion. The PCL alsoacts as a tether on the medical condyle of the femur, keeping the medialcondyle in contact with the medial meniscus. Together these twoligaments are vitally important to the stability of the knee joint,especially in contact sports and those that involve fast changes indirection and twisting and pivoting movements. Therefore a torn orabsent ACL has serious implications for the stability and function forthe knee joint. In other orthopaedic fields, surgeons usually recommendACL replacement surgery for a torn ACL because without the ACL, thefemorotibial joint becomes unstable. It is assumed that this instabilityleads to meniscus and cartilage damage. Unfortunately, the ACL issacrificed in TKA.

Known TKA implants provide for posterior stabilization, but not anteriorstabilization. What is needed, therefore, is a TKA implant that providesfor anterior stabilization in the absence of a surgically removed ACLwhile also accommodating a retained PCL.

INTRODUCTION TO THE INVENTION

Currently, most TKA patients do not receive an implant that replaces thefunctionality of an absent ACL. Specifically, prior art implants do notresist anterior thrust of the femur relative to the tibia, and suchresistance is needed to achieve optimal knee joint functionality.

Referring to FIG. 1, a normal knee joint includes the ACL and PCL. For anormal joint, the ACL is operative to pull the femur anterior while theknee joint is moved toward full extension. Conversely, the PCL isoperative to pull the femur posterior while the knee joint is movedtoward full flexion. As can be seen in FIG. 1, the normal knee jointproximate full extension demonstrates the femur contacts the anterioraspect of the tibia and the patella is in contact with the femur. Thisis in stark contrast to the position of the femur and patella in a PCRTKA.

Referring to FIG. 2, a PCR TKA allows the PCL to remain intact and topull the femur in the posterior direction with flexion, but without thecounteracting forces otherwise attributable to the ACL. In a PS TKA, thecam/post mechanisms force the femur in the posterior direction withincreasing knee flexion, but from flexion to full extension anteriorstabilization does not exist in present day total knee implant. At fullextension, the femoral condyle of both PS and PCR TKA contact the tibialinsert significantly more posterior than the normal knee, leading topatellar component separation from the femoral component and duringactivity, the femoral component remains posterior throughout the motion.

The present knee implant system provides for joint motion that moreclosely mimics the proper function of a natural human knee in part byreplacing the function of a healthy anterior cruciate ligament. In oneembodiment, the knee implant comprises: a femoral component, the femoralcomponent having a first surface attachable to a femur and a secondsurface wherein the second surface includes a pair of substantiallyparallel articular condyles with a slot therebetween, an anterior cam(symmetric, asymmetric, sloped, elongated, round, or variable shapesdepending on the angle between the femur and the tibia) extendingbetween the condyles and through the slot; a tibial component attachableto a tibia; and a bearing component disposed between the tibialcomponent and the femoral component, the bearing component having afirst surface attached to the tibial component and a second articulatingsurface that includes two recessed bearing surfaces such that thefemoral component is rotatably and slidably engaged with the femoralcomponent condyles, and wherein the bearing surfaces are separated by aspine protruding from between the bearing surfaces and wherein the spineengages with the cam at certain flexion angles of the knee implant suchthat the spine contacts the cam to force the femoral component in theanterior direction during extension. At full extension, this cam/postengagement will ensure that the femoral condyles contact the tibialinsert on the anterior aspect. During flexion the cam will release fromthe post until engagement no longer exists. Then, the PCL will pull thefemur in the posterior direction. The anterior cam/post mechanism willwork in unison with the PCL to provide stability to the knee joint.Subjects having an AS TKA will experience an anterior thrust of thefemoral component during extension activities, such as chair-rise,stair-climb and during walking.

It is a first aspect of the present invention to provide a total kneeimplant prosthesis comprising: (a) a posterior retaining ligamentfemoral component including a pair of condyles interposed by an opening,the femoral component also including an anterior cam; and (b) aposterior retaining ligament tibial component, the tibial componentincluding a post and a pair of condyle depressions.

In a more detailed embodiment of the first aspect, the posteriorretaining ligament tibial component includes a tibial tray and a tibialtray insert. In yet another more detailed embodiment, the tibial trayinsert is a mobile bearing insert. In a further detailed embodiment, thetibial tray insert is a fixed bearing insert. In still a furtherdetailed embodiment, the tibial tray insert includes the pair of condyledepressions, and the tibial tray includes the post. In a more detailedembodiment, the tibial tray insert includes the pair of condyledepressions, and the tibial tray insert includes the post. In a moredetailed embodiment, the post is separable from both the tibial trayinsert and the tibial tray. In another more detailed embodiment, theanterior cam is mobile bearing with respect to at least one of the pairof condyles. In still another more detailed embodiment, the anterior camis fixed bearing with respect to the pair of condyles.

In yet another more detailed embodiment of the first aspect, the tibialtray insert comprises independent pieces, a first independent pieceincludes a medial condyle depression of the pair of condyle depressions,and a second independent piece includes a lateral condyle depression ofthe pair of condyle depressions, wherein at least one of the firstindependent piece and the second independent piece is mobile bearingwith respect to the tibial tray. In still another more detailedembodiment, an anterior surface of the post is planar and substantiallyvertical. In a further detailed embodiment, an anterior surface of thepost is sloped upward from anterior to posterior. In still a furtherdetailed embodiment, an anterior surface of the post is substantiallyplanar and angled to face toward a first of the pair of condyledepressions and away from a second of the pair of condyle depressions.In a more detailed embodiment, an anterior surface of the post includesa helical groove. In a more detailed embodiment, an anterior surface ofthe post includes a helical projection. In another more detailedembodiment, the helical projection is at least one of symmetrical andasymmetrical. In yet another more detailed embodiment, the helicalprojection is asymmetrical and a lateral portion of the helicalprojection protrudes outward on a lateral side more than on a medialside.

In a more detailed embodiment of the first aspect, an anterior surfaceof the post is sloped upward from posterior to anterior. In yet anothermore detailed embodiment, an anterior surface of the anterior cam isrounded and substantially perpendicularly oriented with respect to thepair of condyles. In a further detailed embodiment, an anterior surfaceof the anterior cam is planar and angled to face toward a first of thepair of condyles and away from a second of the pair of condyles. In amore detailed embodiment, an anterior surface of the anterior cam isplanar and substantially perpendicularly oriented with respect to thepair of condyles. In a more detailed embodiment, an anterior surface ofthe anterior cam is rounded and angled to face toward a first of thepair of condyles and away from a second of the pair of condyles. Inanother more detailed embodiment, an anterior surface includes aprojection to be received within the helical groove in the post. In yetanother more detailed embodiment, an anterior surface of the anteriorcam includes a helical projection. In still another more detailedembodiment, the helical projection is at least one of symmetrical andasymmetrical.

In yet another more detailed embodiment of the first aspect, the helicalprojection is asymmetrical and a lateral portion of the helicalprojection protrudes outward on a lateral side more than on a medialside. In still another more detailed embodiment, the post includes abase having a cross-section larger than a cross-section at a top of thepost farthest from the tibial tray. In a further detailed embodiment,the tibial tray includes a projection that extends into an area boundedby the tibial tray insert, and the post is mounted to the projection. Instill a further detailed embodiment, the post is fixed bearing withrespect to the projection. In a more detailed embodiment, post isbetween 0.125 millimeters and 50 millimeters in length from anterior toposterior. In a more detailed embodiment, post is between 0.125millimeters and 50 millimeters in width from medial to lateral. Inanother more detailed embodiment, post is between 0.125 millimeters and50 millimeters in height from superior to inferior. In yet another moredetailed embodiment, the anterior cam is resilient.

In a more detailed embodiment of the first aspect, the anterior camincludes a shock absorber. In yet another more detailed embodiment, theanterior cam includes a spring. In a further detailed embodiment, theanterior cam includes at least two springs, where at least two of thesprings have symmetrical spring coefficient. In still a further detailedembodiment, the anterior cam includes at least a medial spring and alateral spring, where the medial spring and the lateral spring haveasymmetrical spring rates. In a more detailed embodiment, a spring rateof the medial spring is lower than a spring rate of the lateral spring.In a more detailed embodiment, the post is resilient. In another moredetailed embodiment, the post includes a shock absorber. In yet anothermore detailed embodiment, the post includes a spring. In still anothermore detailed embodiment, the post includes at least two springs, whereat least two of the springs have symmetrical spring coefficient.

In yet another more detailed embodiment of the first aspect, the postincludes at least a medial spring and a lateral spring, where the medialspring and the lateral spring have asymmetrical spring rates. In stillanother more detailed embodiment, a spring rate of the medial spring islower than a spring rate of the lateral spring. In a further detailedembodiment, at least one of the tibial tray and the tibial tray insertincludes a projection, and the post includes a plurality of cavities,each of the plurality of cavities sized to separately accommodate atleast a portion of the projection to secure the post to at least one ofthe tibial tray and the tibial tray insert. In still a further detailedembodiment, the post includes a projection, and at least one of thetibial tray and the tibial tray insert includes a plurality of cavities,each of the plurality of cavities adapted to house a portion of theprojection to secure the post to at least one of the tibial tray and thetibial tray insert. In a more detailed embodiment, the anterior cam isat least one of inset with respect to the medial and lateral condyles,flush with respect to the medial and lateral condyles, and projectsoutward with respect to the medial and lateral condyles. In a moredetailed embodiment, the femoral component includes a projection, andthe anterior cam includes a plurality of cavities, each of the pluralityof cavities sized to separately accommodate at least a portion of theprojection to secure the anterior cam to the femoral component. Inanother more detailed embodiment, the anterior cam includes aprojection, and the femoral component includes a plurality of cavities,each of the plurality of cavities sized to separately accommodate atleast a portion of the projection to secure the anterior cam to thefemoral component.

It is a second aspect of the present invention to provide a posteriorcruciate ligament retaining knee implant prosthesis comprising: (a) afemoral component including a medial condyle and a lateral condyleseparated from one another by an intercondylar channel adapted toaccommodate throughput of a native cruciate ligament, both the medialcondyle and the lateral condyle posteriorly terminate individually, themedial condyle including a medial condyle bearing surface and thelateral condyle including a lateral condyle bearing surface, the femoralcomponent including an anterior post; and (b) a tibial componentincluding a medial condyle receiver having a medial condyle receiverbearing surface, the tibial component also including a lateral condylereceiver having a lateral condyle receiver bearing surface, the tibialcomponent including an anterior cam.

In a more detailed embodiment of the second aspect, the posteriorretaining ligament tibial component includes a tibial tray and a tibialtray insert. In yet another more detailed embodiment, the tibial trayinsert is a mobile bearing insert. In a further detailed embodiment, thetibial tray insert is a fixed bearing insert. In still a furtherdetailed embodiment, the tibial tray insert includes the pair of condyledepressions, and the tibial tray includes the anterior cam. In a moredetailed embodiment, the tibial tray insert includes the pair of condyledepressions, and the tibial tray insert includes the anterior cam. In amore detailed embodiment, the anterior cam is separable from both thetibial tray insert and the tibial tray. In another more detailedembodiment, the post is mobile bearing with respect to at least one ofthe pair of condyles. In still another more detailed embodiment, thepost is fixed bearing with respect to the pair of condyles.

In yet another more detailed embodiment of the second aspect, the tibialtray insert comprises independent pieces, a first independent pieceincludes a medial condyle depression of the pair of condyle depressions,and a second independent piece includes a lateral condyle depression ofthe pair of condyle depressions, wherein at least one of the firstindependent piece and the second independent piece is mobile bearingwith respect to the tibial tray. In still another more detailedembodiment, an anterior surface of the post is planar and substantiallyvertical. In a further detailed embodiment, an anterior surface of thepost is sloped upward from anterior to posterior. In still a furtherdetailed embodiment, an anterior surface of the anterior cam issubstantially planar and angled to face toward a first of the pair ofcondyle depressions and away from a second of the pair of condyledepressions. In a more detailed embodiment, an anterior surface of thepost includes a helical groove. In a more detailed embodiment, ananterior surface of the post includes a helical projection. In anothermore detailed embodiment, the helical projection is at least one ofsymmetrical and asymmetrical. In yet another more detailed embodiment,the helical projection is asymmetrical and a lateral portion of thehelical projection protrudes outward on a lateral side more than on amedial side.

In a more detailed embodiment of the second aspect, an anterior surfaceof the post is sloped upward from posterior to anterior. In yet anothermore detailed embodiment, an anterior surface of the post is rounded andsubstantially perpendicularly oriented with respect to the pair ofcondyles. In a further detailed embodiment, an anterior surface of thepost is planar and angled to face toward a first of the pair of condylesand away from a second of the pair of condyles. In a more detailedembodiment, an anterior surface of the post is planar and substantiallyperpendicularly oriented with respect to the pair of condyles. In a moredetailed embodiment, an anterior surface of the post is rounded andangled to face toward a first of the pair of condyles and away from asecond of the pair of condyles. In another more detailed embodiment, ananterior surface includes a projection to be received within the helicalgroove in the anterior cam. In yet another more detailed embodiment, ananterior surface of the post includes a helical projection. In stillanother more detailed embodiment, the helical projection is at least oneof symmetrical and asymmetrical.

In yet another more detailed embodiment of the first aspect, the helicalprojection is asymmetrical and a lateral portion of the helicalprojection protrudes outward on a lateral side more than on a medialside. In still another more detailed embodiment, the post includes abase having a cross-section larger than a cross-section at a top of thepost farthest from the femoral attachment location. In a furtherdetailed embodiment, the tibial tray includes a projection that extendsinto an area bounded by the tibial tray insert, and the anterior cam ismounted to the projection. In still a further detailed embodiment, theanterior cam is fixed bearing with respect to the projection. In a moredetailed embodiment, post is between 0.125 millimeters and 50millimeters in length from anterior to posterior. In a more detailedembodiment, post is between 0.125 millimeters and 50 millimeters inwidth from medial to lateral. In another more detailed embodiment, postis between 0.125 millimeters and 50 millimeters in height from superiorto inferior. In yet another more detailed embodiment, the anterior camis resilient.

In a more detailed embodiment of the second aspect, the anterior camincludes a shock absorber. In yet another more detailed embodiment, theanterior cam includes a spring. In a further detailed embodiment, theanterior cam includes at least two springs, where at least two of thesprings have symmetrical spring coefficient. In still a further detailedembodiment, the anterior cam includes at least a medial spring and alateral spring, where the medial spring and the lateral spring haveasymmetrical spring rates. In a more detailed embodiment, a spring rateof the medial spring is lower than a spring rate of the lateral spring.In a more detailed embodiment, the post is resilient. In another moredetailed embodiment, the post includes a shock absorber. In yet anothermore detailed embodiment, the post includes a spring. In still anothermore detailed embodiment, the post includes at least two springs, whereat least two of the springs have symmetrical spring coefficient.

In yet another more detailed embodiment of the second aspect, the postincludes at least a medial spring and a lateral spring, where the medialspring and the lateral spring have asymmetrical spring rates. In stillanother more detailed embodiment, a spring rate of the medial spring islower than a spring rate of the lateral spring. In a further detailedembodiment, at least one of the tibial tray and the tibial tray insertincludes a projection, and the anterior cam includes a plurality ofcavities, each of the plurality of cavities sized to separatelyaccommodate at least a portion of the projection to secure the anteriorcam to at least one of the tibial tray and the tibial tray insert. Instill a further detailed embodiment, the anterior cam includes aprojection, and at least one of the tibial tray and the tibial trayinsert includes a plurality of cavities, each of the plurality ofcavities adapted to house a portion of the projection to secure theanterior cam to at least one of the tibial tray and the tibial trayinsert. In a more detailed embodiment, the post is at least one of insetwith respect to the medial and lateral condyles, flush with respect tothe medial and lateral condyles, and projects outward with respect tothe medial and lateral condyles. In a more detailed embodiment, thefemoral component includes a projection, and the post includes aplurality of cavities, each of the plurality of cavities sized toseparately accommodate at least a portion of the projection to securethe post to the femoral component. In another more detailed embodiment,the post includes a projection, and the femoral component includes aplurality of cavities, each of the plurality of cavities sized toseparately accommodate at least a portion of the projection to securethe post to the femoral component.

It is a third aspect of the present invention to provide a total kneeimplant prosthesis comprising: (a) a posterior retaining ligamentfemoral component including a pair of condyles interposed by an openingto accommodate a posterior cruciate ligament, the femoral component alsoincluding an anterior cam; and (b) a posterior retaining ligament tibialcomponent, the tibial component including a post and a pair of condyledepressions, where at least one of the anterior cam and the post isspring biased.

It is a fourth aspect of the present invention to provide a posteriorcruciate retaining total knee femoral implant prosthesis comprising aposterior retaining ligament femoral component including a pair ofcondyles interposed by an opening to accommodate a posterior cruciateligament, the femoral component also including an anterior cam.

It is a fifth aspect of the present invention to provide a posteriorcruciate retaining total knee femoral implant prosthesis comprising aposterior retaining ligament femoral component including a pair ofcondyles interposed by an opening to accommodate a posterior cruciateligament, the femoral component also including an anterior post.

It is a sixth aspect of the present invention to provide a posteriorcruciate retaining total knee tibial implant prosthesis comprising aposterior retaining ligament tibial component including the tibialcomponent including a cam and a pair of condyle depressions.

It is a seventh aspect of the present invention to provide a posteriorcruciate retaining total knee tibial implant prosthesis comprising aposterior retaining ligament tibial component including the tibialcomponent including a cam and a pair of condyle depressions.

It is an eighth aspect of the present invention to provide a total kneeimplant prosthesis comprising: (a) a posterior retaining ligamentfemoral component including a pair of condyles interposed by an openingto accommodate a posterior cruciate ligament, the femoral component alsoincluding at least one projection extending from at least one of thecondyles; and (b) a posterior retaining ligament tibial component, thetibial component including a pair of condyle depressions to receive thepair of condyles, at least one of the pair of condyle depressionsincludes at least one cavity, each of the at least one cavity adapted toreceive one of the at least one projection from the femoral component.

It is a ninth aspect of the present invention to provide a total kneeimplant prosthesis comprising: (a) a posterior retaining ligamentfemoral component including a pair of condyles interposed by an openingto accommodate a posterior cruciate ligament, the femoral component alsoincluding at least one cavity within at least one of the condyles; and(b) a posterior retaining ligament tibial component, the tibialcomponent including a pair of condyle depressions to receive the pair ofcondyles, at least one of the pair of condyle depressions includes atleast one projection, each of the at least one cavity adapted to receiveone of the at least one projection from the tibial component.

It is a tenth aspect of the present invention to provide a total kneeimplant prosthesis comprising: (a) a posterior retaining ligamentfemoral component including a medial condyle and a lateral condyleinterposed by an opening to accommodate a posterior cruciate ligament,the medial condyle including at least one projection, and the lateralcondyle including at least one projection; and (b) a posterior retainingligament tibial component, the tibial component including a medialcondyle receiver and a lateral condyle receiver correspondinglyoperative to receive the medial and lateral condyles, the medial condylereceiver including at least one cavity to receive the at least oneprojection of the medial condyle, the lateral condyle receiver includingat least one cavity to receive the at least one projection of thelateral condyle.

It is an eleventh aspect of the present invention to provide a totalknee implant prosthesis comprising: (a) a posterior retaining ligamentfemoral component including a medial condyle and a lateral condyleinterposed by an opening to accommodate a posterior cruciate ligament,the medial condyle including at least one cavity, and the lateralcondyle including at least one cavity; and (b) a posterior retainingligament tibial component, the tibial component including a medialcondyle receiver and a lateral condyle receiver correspondinglyoperative to receive the medial and lateral condyles, the medial condylereceiver including at least one projection to be received within the atleast one cavity of the medial condyle, the lateral condyle receiverincluding at least one projection to be received within the at least onecavity of the lateral condyle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray image of a human knee joint proximate full extension.

FIG. 2 is an X-ray image of a prosthetic knee joint proximate fullextension.

FIGS. 3A-3D are exemplary diagrams showing different degrees of flexionand extension of a natural knee and a corresponding placement of aprosthetic joint when certain flexion or extension occurs.

FIG. 4 is an exploded view of a first exemplary embodiment of aposterior cruciate retaining replacement knee providing anteriorstabilization.

FIG. 5 is a bottom view of an exemplary femoral component in accordancewith the present disclosure.

FIG. 6 is a bottom view of another exemplary femoral component inaccordance with the present disclosure.

FIG. 7 is a bottom view of a further exemplary femoral component inaccordance with the present disclosure.

FIG. 8 is a bottom view of yet another exemplary femoral component inaccordance with the present disclosure.

FIG. 9 is a profile view of an exemplary distal component in accordancewith the present disclosure.

FIG. 10 is a profile view of another exemplary distal component inaccordance with the present disclosure.

FIG. 11 is a profile view of a further exemplary distal component inaccordance with the present disclosure.

FIG. 12 is a top view of an exemplary tibial tray insert in accordancewith the present disclosure.

FIG. 13 is a top view of another exemplary tibial tray insert inaccordance with the present disclosure.

FIG. 14 is a bottom view of still a further exemplary femoral componentin accordance with the present disclosure.

FIG. 15 is a top view of another exemplary femoral tibial tray insert inaccordance with the present disclosure.

FIG. 16 is a top view of yet another exemplary tibial tray insert inaccordance with the present disclosure.

FIG. 17 is a bottom view of another exemplary femoral component inaccordance with the present disclosure.

FIG. 18 is a top view of still a further exemplary tibial tray insert inaccordance with the present disclosure.

FIG. 19 is a profile view of an exemplary tibial component in accordancewith the present disclosure.

DETAILED DESCRIPTION

The exemplary embodiments of the present disclosure are described andillustrated below to encompass prosthetic knee joints and knee jointcomponents, as well as methods of implanting and reconstructing kneejoints. Of course, it will be apparent to those of ordinary skill in theart that the preferred embodiments discussed below are exemplary innature and may be reconfigured without departing from the scope andspirit of the present invention. However, for clarity and precision, theexemplary embodiments as discussed below may include optional steps,methods, and features that one of ordinary skill should recognize as notbeing a requisite to fall within the scope of the present invention.

Referencing FIGS. 3A-3D, a series of representations are shown of ageneric human anatomy below the torso comprising a femur 10 and a tibia12 that represent the position of the femur with respect to the tibia asthe knee joint 14 flexes. FIG. 1A shows the femur 10 and tibia 12 inaxial alignment with respect to a TKA axis 16 when the knee joint 14 isin complete extension. Likewise, FIG. 3A also shows the common positionof a femoral component 20 and a tibial component 22 that may be used ina total knee arthroplasty when the prosthetic knee joint is in fullextension.

Referring to FIG. 3B, the knee joint 14 is at approximately 45 degreesof flexion. In this manner, the distal portion of the femur 10 has movedforward relative to the tibia, as has the proximal portion of the tibia12. Similarly, in the prosthetic knee joint, 45 degrees of flexioncauses the tibial component 22 to shift forward with respect to the TKAaxis 16 and takes on the angle of the remainder of the tibia. Likewise,the femoral component 20 also shifts forward with respect to the TKAaxis 16, but rolls backward (posteriorly) with respect to the tibialcomponent 22 so that a more posterior portion of the condyles of thefemoral component are seated within a more posterior portion of thetibial component.

Referencing FIG. 3C, continued flexion of the knee joint 14 toapproximately 90 degrees results in further forward motion of the femur10 and tibia 12 with respect to the TKA axis 16. Consistent with thismovement, the femoral component 20 and the tibial component 22 also aremoved further forward with respect to the TKA axis 16, but the femoralcomponent continues to rotate posteriorly and move backward on thetibial component.

Referencing FIG. 3D, continued flexion of the knee joint 14 to maximumflexion of approximately 160 degrees results in maximum forward motionof the femur 10 and tibia 12 with respect to the TKA axis 16. Consistentwith this movement, the femoral component 20 and the tibial component 22also are moved further forward with respect to the TKA axis 16 and thefemoral component continues to rotate posteriorly and move rearward onthe tibial component so that only the most posterior portion of thefemoral component 20 remains in contact with the tibial component 22.

Referring FIG. 4, an exemplary posterior cruciate retaining orthopaedicknee implant 100 for use with total arthroplasty procedures includes afemoral component 102 and a tibial component 104. In this exemplaryembodiment, the tibial component 104 comprises a tibial tray 106 and atibial tray insert 108.

The exemplary posterior cruciate retaining orthopaedic femoral component102 includes a posterior discontinuity or gap 110 between lateral andmedial condyles 112, 114 to allow the femoral component to rotatebetween maximum extension and maximum flexion without impinging theposterior cruciate ligament (PCL), which is retained. In contrast, theanterior cruciate ligament (ACL) is sacrificed or removed during a totalarthroplasty procedure. Those skilled in the art are familiar with theposterior constraint resulting from retention of the posterior cruciateligament, whereas those skilled in the art are also familiar with theabsence of anterior constraint resulting from the absence of theanterior cruciate ligament.

This exemplary femoral component 102 includes two condyles 112, 114 eachhaving an arcuate shape in order to allow for smooth rotation of thefemur with respect to the tibia. In general, the femoral componentincludes an anterior portion 116 and a posterior portion 118 that areshown by the dotted line imaginary boundary. The anterior portion 116includes a front exterior face 120 having a depression 122 adapted toreceive at least a portion of a patella component 123. The depression122 marks the beginning of individual condyle 112, 114 formation. Fromthe top of the front face 120 downward, following the contours of thefront face, the curved nature of begins to take shape and transitioninto individual condyles 112, 114. As the shape of the condyles 112, 114becomes more pronounced, the condyles separate from one another, whichis marked by an arcuate bridge 124 formed at the most proximalconnection point of the condyles. As the shape of the condyles 112, 114continue more distal, past the arcuate bridge 124, the condyles widenand generally flare out on the outer edges. At the same time, thebearing surfaces of the condyles 112, 114 flatten out and do not exhibita uniform arcuate shape from anterior to posterior. However, theposterior discontinuity or gap 110 has a substantially uniform width,resulting in the inner shape and contour of the condyles beingsubstantially the same. Unlike prior art posterior cruciate retainingfemoral components, the exemplary posterior cruciate retaining femoralcomponent 102 includes an anterior cam 126 that engages a post 128 ofthe tibial component 104.

Referring to FIG. 5, the anterior femoral cam 126 of the femoralcomponent 102 may have various shapes. For example, an alternateanterior cam 126′ has a camming surface that is arcuate or rounded as aresult of the cam having a cylindrical shape. Conversely, the anteriorcam 126 could include a camming surface that is substantially flat wherethe cam is in the shape of a square or rectangular peg.

Referring to FIG. 6, in a further alternate exemplary embodiment of thefemoral component 102, the anterior cam 126″ has an inclined arcuate orrounded camming surface as a result of the cam having a hybrid shapemelding a cylindrical half with a conical half. Because the conical halffaces the posterior direction, the conical half comprises the cammingsurface that interacts with the tibial post 128 (see FIG. 4). In thisexemplary embodiment, the camming surface has an inclined slope from themedial condyle 114 to the lateral condyle 112. Conversely, the anteriorcam could embody a trapezoidal shape having a substantially flat, butinclined to slope from the medial condyle 114 to the lateral condyle112.

Referring to FIG. 7, in yet a further alternate exemplary embodiment ofthe femoral component 102, the anterior cam 126″′ has a rounded, helicalshape. In other words, the shape of the anterior cam 126″′ resembles aworm gear having a helical thread. In this exemplary embodiment, thehelical thread increasing in thickness from medial to lateral.Accordingly, as the femoral component is rotated from anterior toposterior, the amount of camming surface contacting the tibial post 128(see FIG. 4) increases concurrently with increased axial rotation of thefemoral component 102.

Referencing FIG. 8, in still a further alternate exemplary embodiment ofthe femoral component 102′, the anterior cam 126″″ has an arcuate orrounded camming surface that is biased to cushion the impact of thecamming surface coming into contact with the tibial post 128 (see FIG.4). In this alternate exemplary embodiment of the femoral component102′, the camming surface is embodied in a separate component 130 of theanterior cam 126″″ that is mounted to a cam retainer 132, which ismounted to the remainder of the femoral component 102′. A pair ofbiasing members 134 interposes the camming surface component 130 and thecam retainer. In this exemplary embodiment, each biasing member 134comprises a helical spring. However, alternate structures may be used inlieu of a helical spring including, without limitation, a resilientbushing or leaf spring.

It is also within the scope of the invention that the medial biasingmember 134M and the lateral biasing member 134L having different biasingstrengths and/or be comprised of different structures or components. Forexample, the medial biasing member 134M may comprise a titanium helicalspring having a spring rate different than that the lateral biasingmember 134L, which comprises a stainless steel leaf spring. In exemplaryform, the medial biasing member 134M includes a spring ratesubstantially less than that of the lateral biasing member 134L so thatupon contact with the tibial post 128, the medial biasing member 134Mcompresses to a greater degree than the lateral biasing member 134L,thus providing a camming surface that is accordingly inclined from themedial condyle 114 to the lateral condyle 112.

Referencing FIGS. 4 and 9, the exemplary tibial tray 106 includes a stem141 that is adapted to be received within the intramedullary canal ofthe tibia. The stem 141 may be cemented or adapted for bone ingrowth topermanently mount the tibial tray 106 to the tibia. Integral with thestem 141 is a platform 142 on which the tibial tray insert 108 ismounted. In this regard, the tibial tray 106 may provide either a fixedbearing interface to lock the orientation of the tibial tray insert 108with the tibial tray 106 or a mobile bearing interface that allows thetibial tray insert 108 to move independent of the tibial tray 106.

A first exemplary tibial tray 106 includes a first cylindricalprojection 140 that extends upward from the platform 142 in a directiongenerally perpendicular to the face of the platform. This firstcylindrical projection 140 is substantially centered fromanterior-to-posterior and lateral-to-medial on the platform 142. Inexemplary form, the projection 140 is received within a cavity 152extending through the tibial tray insert 108, but not received sotightly as to inhibit rotation of the tibial tray insert with respect tothe projection. It is the combination of the projection 140 and thecavity 152 that provides mobile bearing functionality for the tibialcomponent 104. As will be obvious to those skilled in the art, thecavity 152 and the projection 140 may be switched so that the platform142 includes the cavity, while the tray insert 108 includes theprojection.

The tibial tray insert 108 also includes concave bearing surfaces 160,162 that are adapted to receive the medial and lateral condyles 114, 112of the femoral component 102. The two concave bearing surfaces 160, 162are partially separated from one another by a trapezoidal post 164upstanding from the tibial tray insert 108. In this exemplaryembodiment, the post 164 is integrally formed with the tibial trayinsert 108. However, it is also within the scope of the invention thatthe post 164 is separable from the tibial tray insert 108 and itslocation is independent of the location/movement of the tibial trayinsert. The post 164 includes an anterior wall 166 having asubstantially vertical face and a posterior wall 168 having an inclinedface from posterior to anterior. The vertical face of the anterior wall166 is substantially parallel with the anterior-posterior centerline.The anterior wall 166 and posterior wall 168 are separated from oneanother by substantially vertical medial and lateral side walls 170, 172and a horizontal top wall 174.

Referring to FIG. 10, an alternate exemplary fixed bearing tibialcomponent 104′ includes a tibial tray 106′ and a tibial tray insert108′. In this exemplary embodiment, the tibial tray 106′ includes a stem141′ that is adapted to be received within the intramedullary canal ofthe tibia. The stem 141′ may be cemented or adapted for bone ingrowth topermanently mount the tibial tray 106′ to the tibia. Integral with thestem 141′ is a platform 142′ on which the tibial tray insert 108′ ismounted.

The tibial tray insert 108′ also includes concave bearing surfaces 160′,162′ that are adapted to receive the medial and lateral condyles 114,112 of the femoral component 102 (see FIG. 4). The two concave bearingsurfaces 160′, 162′ are partially separated from one another by atrapezoidal post 164′ upstanding from the tibial tray insert 108′. Inthis exemplary embodiment, the post 164′ is integrally formed with thetibial tray insert 108′ and includes an anterior wall 166′ having asubstantially vertical face and a posterior wall 168′ having an inclinedface from posterior to anterior. The vertical face of the anterior wall166′ is substantially parallel with the anterior-posterior centerline.The anterior wall 166′ and posterior wall 168′ are separated from oneanother by substantially vertical medial and lateral side walls 170′,172′ and a horizontal top wall 174′.

Referring to FIG. 11, a further alternate exemplary fixed bearing tibialcomponent 104″ includes a tibial tray 106″ and a tibial tray insert108″. In this exemplary embodiment, the tibial tray 106″ includes a stem141″ that is adapted to be received within the intramedullary canal ofthe tibia. The stem 141″ may be cemented or adapted for bone ingrowth topermanently mount the tibial tray 106″ to the tibia. Integral with thestem 141″ is a platform 142″ on which the tibial tray insert 108″ ismounted.

The tibial tray insert 108″ also includes concave bearing surfaces 160″,162″ that are adapted to receive the medial and lateral condyles 114,112 of the femoral component 102 (see FIG. 4). The two concave bearingsurfaces 160″, 162″ are partially separated from one another by atrapezoidal post 164″ upstanding from the tibial tray insert 108″. Inthis exemplary embodiment, the post 164″ is integrally formed with thetibial tray 106″. However, it is also within the scope of the inventionthat the post 164″ is separable from the tibial tray 106″ andcorrespondingly its location is not dependent upon the variable locationof a mobile bearing tibial tray. The post 164″ includes an arcuateanterior wall 166″ having a substantially vertical face and a posteriorconical wall 168″ having an arcuate, inclined face from posterior toanterior. The anterior wall 166″ and posterior wall 168″ are joinedseamlessly to one another and transition at the top to a flat,substantially horizontal top wall 174″.

Referencing FIGS. 12 and 13, an alternate exemplary tibial tray insert184 for use in combination with the exemplary femoral components 102includes a tibial post 180, 182 and adjacent medial and lateral condyles186, 188. The exemplary tibial post 180,182, in contrast to theforegoing exemplary tibial posts 164, includes an anterior wall angledother than parallel with respect to the anterior-posterior centerline tothe tibial tray insert 184.

Referring to FIG. 12, a first exemplary post 180 includes a generallytrapezoidal shape exposed portion above the surface of the tibial trayinsert 184. The post comprises a flat, substantially vertical posteriorsurface 190 and flat, substantially vertical side surfaces 192, 194. Ananterior surface 196 is flat and substantially vertical, but is angled20 degrees with respect to the anterior-posterior centerline. In otherwords, the leading or anterior edge on the lateral side of the post 180is closer to the front of the tibial tray insert 184 than is the leadingor anterior edge on the medial side of the post. In this manner, as thecamming surface of the femoral component contacts the anterior face ofthe post 180, the angle of the anterior surface cause the femoralcomponent to rotate medially.

Referring to FIG. 13, a second exemplary post 182 includes a generallytrapezoidal shape exposed portion above the surface of the tibial trayinsert 184. The post comprises a flat, substantially vertical posteriorsurface 200 and flat, substantially vertical side surfaces 202, 204. Ananterior surface 206 is inclined from anterior-to-posterior and angledwith respect to the anterior-posterior centerline of the tibial trayinsert 184. In this exemplary embodiment, the anterior surface is angled20 degrees with respect to the anterior-posterior centerline and angled70 degrees with respect to horizontal. In other words, the bottom cornerof the anterior surface and the lateral side 188 is closer to the frontof the tibial tray insert 184 than is the bottom corner of the anterioredge on the medial side of the post 182. In this manner, as the cammingsurface of the femoral component contacts the anterior face of the post180, the angle and decline of the anterior surface cause the femoralcomponent to rotate medially.

Referring to FIGS. 14-16, a second exemplary posterior cruciateretaining orthopaedic knee implant for use with total arthroplastyprocedures includes a femoral component 302 and a tibial component 304.In this exemplary embodiment, the tibial component 304 comprises atibial tray (not shown) and a tibial tray insert 306, 308.

The exemplary posterior cruciate retaining orthopaedic femoral component302 include a posterior discontinuity or gap 310 between lateral andmedial condyles 312, 314 to allow the femoral component to rotatebetween maximum extension and maximum flexion without impinging theposterior cruciate ligament, which is retained. Those skilled in the artare familiar with the posterior constraint resulting from retention ofthe posterior cruciate ligament, whereas those skilled in the art arealso familiar with the absence of anterior constraint resulting from theabsence of the anterior cruciate ligament.

Referring specifically to FIG. 14, this exemplary femoral component 302includes two condyles 312, 314 each having an arcuate shape in order toallow for smooth rotation of the femur with respect to the tibia. As theshape of the condyles 312, 314 becomes more pronounced, the condylesseparate from one another, which is marked by an arcuate bridge 324formed at the most proximal connection point of the condyles. As theshape of the condyles 312, 314 continues distally, past the arcuatebridge 324, the condyles widen and generally flare out on the outeredges. At the same time, the bearing surfaces of the condyles 312, 314flatten out and do not exhibit a uniform arcuate shape from anterior toposterior. However, the posterior discontinuity or gap 310 has asubstantially uniform width, resulting in the inner shape and contour ofthe condyles being substantially the same. Unlike prior art posteriorcruciate retaining femoral components, the exemplary posterior cruciateretaining femoral component 302 includes an anterior post 326 thatengages a tibial cam 328 of the tibial component 304.

The anterior femoral post 326 of the femoral component 302 is mounted toa recessed bracket 330 extending between the condyles 312, 314 proximatethe bridge 324. In exemplary form, the femoral post 326 includes arectangular cross-section and a sloped posterior face 332.

Referring to FIG. 15, the tibial component 304 may include a firstexemplary tibial tray insert 306 having concave bearing surfaces 360,362 that are adapted to receive the medial and lateral condyles 314, 312of the femoral component 302. The two concave bearing surfaces 360, 362are partially separated from one another by the tibial cam 328upstanding from the tibial tray insert 306. In this exemplaryembodiment, the cam 328 is integrally formed with the tibial tray insert306. However, it is also within the scope of the invention that the cam328 is separable from the tibial tray insert 306 and correspondinglymoves independent of the tibial tray insert. The cam 328 includes arounded exterior surface 334, which is angled other than perpendicularwith respect to the anterior-posterior centerline. In this exemplaryembodiment, the cam 328 is angled at 20 degrees with respect to theanterior-posterior centerline.

Referring to FIG. 16, the tibial component 304 may include a secondexemplary tibial tray insert 308 having concave bearing surfaces 360,362 that are adapted to receive the medial and lateral condyles 314, 312of the femoral component 302. The two concave bearing surfaces 360, 362are partially separated from one another by the tibial cam 328upstanding from the tibial tray insert 306. In this exemplaryembodiment, the cam 328 is integrally formed with the tibial tray insert306. However, it is also within the scope of the invention that the cam328 is separable from the tibial tray insert 306 and correspondinglymoves independent of the tibial tray insert. The cam 328 includes arounded exterior surface 334, which is perpendicularly angled withrespect to the anterior-posterior centerline.

In operation, the femoral post 326 and tibial cam 328 work together toanteriorly stabilize the orthopaedic knee replacement joint. Presuming arange of motion starting at fully flexion, the condyles 312, 314 of thefemoral component 302 rotate from posterior to anterior so thateventually the posterior face 332 of the post 326 engages the anteriorrounded exterior surface 334 of the femoral cam 328 to anteriorlystabilize the knee joint at near full extension up through fullextension. When the femoral component 302 is rotated from anterior toposterior from full extension toward full flexion, the femoral post 326gradually disengages against the tibial cam 326 so that posteriorstability is provided by the retained posterior cruciate ligament atnear full flexion toward full flexion.

In the circumstance where the femoral post 326 is angled toward themedial condyle 362, presuming a range of motion starting at fullyflexion, the condyles 312, 314 of the femoral component 302 rotate fromposterior to anterior so that eventually the posterior face 332 of thepost 326 engages the anterior rounded exterior surface 334 of thefemoral cam 328 on the lateral side and rotates the femoral component302 medially combined with anterior stabilization the knee joint at nearfull extension up through full extension. Continued extension beyondinitial engagement between the femoral post 326 and the tibial cam 328results in more pronounced rotation so that eventually the femoral post326 rides square upon the tibial cam 328 at maximum extension. When thefemoral component 302 is rotated from anterior to posterior from fullextension toward full flexion, the femoral post 326 gradually disengagesagainst the tibial cam 326 combined with lateral rotation of the femoralcomponent 302 so that posterior stability is provided by the retainedposterior cruciate ligament at near full flexion toward full flexion.

Referring to FIGS. 17 and 18, a third exemplary posterior cruciateretaining orthopaedic knee implant for use with total arthroplastyprocedures includes a femoral component 402 and a tibial component (nottotally shown). In this exemplary embodiment, the tibial componentcomprises a tibial tray (not shown) and a tibial tray insert 406. Theexemplary posterior cruciate retaining orthopaedic femoral component 402include a posterior discontinuity or gap 410 between lateral and medialcondyles 412, 414 to allow the femoral component to rotate betweenmaximum extension and maximum flexion without impinging the posteriorcruciate ligament, which is retained. Those skilled in the art arefamiliar with the posterior constraint resulting from retention of theposterior cruciate ligament, whereas those skilled in the art are alsofamiliar with the absence of anterior constraint resulting from theabsence of the anterior cruciate ligament.

Referring specifically to FIG. 17, this exemplary femoral component 402includes two condyles 412, 414 each having an arcuate shape in order toallow for smooth rotation of the femur with respect to the tibia. As theshape of the condyles 412, 414 becomes more pronounced, the condylesseparate from one another, which is marked by an arcuate bridge 424formed at the most proximal connection point of the condyles. As theshape of the condyles 412, 414 continues distally, past the arcuatebridge 424, the condyles widen and generally flare out on the outeredges. At the same time, the bearing surfaces of the condyles 412, 414flatten out and do not exhibit a uniform arcuate shape from anterior toposterior. However, unlike prior art posterior cruciate retainingfemoral components, the exemplary posterior cruciate retaining femoralcomponent 402 includes a lateral condyle cylindrical projection 426 anda medial condyle cylindrical projection 428.

Referring to FIG. 18, the tibial tray insert 406 includes lateral andmedial condyle receivers 434, 436 that are adapted to receive thelateral and medial condyles 412, 414 of the femoral component 402. Inexemplary form, each of the condyle receivers includes a correspondingcavity 430, 432 adapted to receive the condyle projections 426, 428 ofthe femoral component.

In operation, the femoral projections 426, 428 and tibial cavities 430,432 work together to anteriorly stabilize the orthopaedic kneereplacement joint. Presuming a range of motion starting at fullyflexion, the condyles 412, 414 of the femoral component 402 rotate fromposterior to anterior so that eventually the lateral projection 426 onthe lateral condyle 412 engages the lateral cavity 430 in the lateralcondyle receiver 434 to inhibit sliding of the lateral condyle withrespect to the lateral condyle receiver. Continued rotation 334 of thefemoral component 402 with respect to the tibial tray insert 406 causesthe femoral component to pivot about the lateral condyle receiver cavity430 so that the femoral component rotates medially until the medialcondyle projection 428 is received within the medial condyle cavity 432.The corresponding inhabitation of sliding as the femoral component 402is rotated provides anterior stability as the knee joint is near fullextension through full extension. Conversely, as the femoral component402 is rotated from anterior to posterior from full extension towardfull flexion, the femoral condyle projections 426, 428 disengage fromthe cavities 430 432 of the tibial tray insert 406 so that posteriorstability is provided by the retained posterior cruciate ligament atnear full flexion toward full flexion.

Referring to FIG. 19, an exemplary tibial component 500 includes atibial tray insert 502 mounted to a tibial tray 504. In this exemplarytibial component, an anterior post 506 is mounted to either the tibialtray insert 502 or the tibial tray 504 so that an anterior cam of afemoral component (not shown) engages the post to pull the femuranterior with respect to the tibia. The exemplary post 506 includes aposterior aspect 508 and an anterior aspect 510 that are interposed by aresilient material or one or more springs 512. In this exemplaryembodiment, the post 506 includes a pair of springs 512, one on themedial side and one on the lateral side. More specifically, the springrate of the medial spring is less than the spring rate of the lateralspring so that contact with the anterior cam of the femoral component isoperative to push the anterior aspect 510 on the medial side moreposterior than the lateral side of the anterior aspect. It is to beunderstood, however, that only one or more than two springs may beutilized. In addition, when multiple springs are utilized, the springrates may be uniform or varied. In addition or in lieu of springs,resilient materials may be utilized that have different compressionratings or the same material may be utilized. Those skilled in the artwill understand the plethora of options available by using a resilientmaterial or a spring to interpose the anterior and posterior aspects ofthe tibial post.

The exemplary femoral components of the exemplary embodiments may befabricated from a hard and durable biocompatible material such as atitanium alloy, cobalt chrome alloy, alumina ceramic or zirconiaceramic. However, those of skill in the art will appreciate that anymaterial can be used for this or the other components of a total kneeimplant while remaining within the scope of the present invention.

The exemplary tibial components may be fabricated from a biocompatiblematerial such as, without limitation, polyethylene, ultra high molecularweight polyethylene, highly cross-linked ultra high molecular weightpolyethylene, a ceramic, and any biocompatible metal.

While the foregoing exemplary embodiments have been described to have aseparable tibial tray and a tibial tray insert, it is to be understoodthat the tibial tray may include condyle receiver bearing surfaces thatobviate the need for a separate tibial tray insert.

Following from the above description and invention summaries, it shouldbe apparent to those of ordinary skill in the art that, while themethods and apparatuses herein described constitute exemplaryembodiments of the present invention, the invention contained herein isnot limited to this precise embodiment and that changes may be made tosuch embodiments without departing from the scope of the invention asdefined by the claims. Additionally, it is to be understood that theinvention is defined by the claims and it is not intended that anylimitations or elements describing the exemplary embodiments set forthherein are to be incorporated into the interpretation of any claimelement unless such limitation or element is explicitly stated.Likewise, it is to be understood that it is not necessary to meet any orall of the identified advantages or objects of the invention disclosedherein in order to fall within the scope of any claims, since theinvention is defined by the claims and since inherent and/or unforeseenadvantages of the present invention may exist even though they may nothave been explicitly discussed herein.

What is claimed is:
 1. A total knee implant prosthesis comprising: aposterior ligament retaining femoral component including a pair ofcondyles interposed by an opening, the femoral component being free fromany posterior cam; and a posterior ligament retaining tibial component,the tibial component including a pair of condyle depressions; wherein:one of the components includes a post having an anterior surface and theother of the components includes an anterior cam having an anteriorsurface; the anterior cam and post are sized, shaped and positioned sothat the anterior cam and the anterior surface of the post are engagedwhen the knee is fully extended and the anterior cam and the anteriorsurface of the post are disengaged during at least part of flexion ofthe knee.
 2. The total knee implant prosthesis of claim 1, wherein thetibial tray insert is a mobile bearing insert.
 3. The total knee implantprosthesis of claim 1, wherein the tibial component includes a tibialtray and a tibial tray insert and wherein the tibial tray insert is afixed bearing insert.
 4. The total knee implant prosthesis of claim 1,wherein the tibial component includes a tibial tray and a tibial trayinsert and wherein: the tibial tray insert includes the pair of condyledepressions; and the tibial tray includes the post.
 5. The total kneeimplant prosthesis of claim 4, wherein the post is separable from boththe tibial tray insert and the tibial tray.
 6. The total knee implantprosthesis of claim 1, wherein: the tibial tray insert includes the pairof condyle depressions; and the tibial tray insert includes the post. 7.The total knee implant prosthesis of claim 6, wherein the post isseparable from both the tibial tray insert and the tibial tray.
 8. Thetotal knee implant prosthesis of claim 1, wherein: the tibial trayinsert comprises independent pieces; a first independent piece includesa medial condyle depression of the pair of condyle depressions; and asecond independent piece includes a lateral condyle depression of thepair of condyle depressions; wherein at least one of the firstindependent piece and the second independent piece is mobile bearingwith respect to the tibial tray.
 9. The total knee implant prosthesis ofclaim 1, wherein an anterior surface of the post is planar andsubstantially vertical.
 10. The total knee implant prosthesis of claim1, wherein an anterior surface of the post is sloped upward fromanterior to posterior.
 11. The total knee implant prosthesis of claim 1,wherein an anterior surface of the post is substantially planar andangled to face toward a first of the pair of condyle depressions andaway from a second of the pair of condyle depressions.
 12. The totalknee implant prosthesis of claim 1, wherein an anterior surface of thepost includes a helical groove.
 13. The total knee implant prosthesis ofclaim 12, wherein an anterior surface of the anterior cam includes aprojection to be received within the helical groove.
 14. The total kneeimplant prosthesis of claim 1, wherein an anterior surface of the postincludes a helical projection.
 15. The total knee implant prosthesis ofclaim 14, wherein the helical projection is at least one of symmetricaland asymmetrical.
 16. The total knee implant prosthesis of claim 1,wherein an anterior surface of the post is sloped upward from posteriorto anterior.
 17. The total knee implant prosthesis of claim 1, whereinan anterior surface of the anterior cam is rounded.
 18. The total kneeimplant prosthesis of claim 1, wherein an anterior surface of theanterior cam is planar.
 19. The total knee implant prosthesis of claim1, wherein an anterior surface of the anterior cam includes a helicalgroove.
 20. The total knee implant prosthesis of claim 19, wherein theanterior surface of the post includes a projection to be received withinthe helical groove.